Coat a 13-by-9-inch baking dish with vegetable cooking spray. Combine the reserved pasta, the tomato sauce, and pepper flakes. Sprinkle the top with the mozzarella. Follow the freezing directions for Roasted-Vegetable and Feta Ziti. (See link to recipe, above.)
To cook, place the frozen, covered baking dish of pasta in the oven and set the temperature to 350° F, bake for 1 hour. (To prevent cracking, never put a cold dish into a preheated oven.) Once the temperature reaches 350° F, bake for 1 hour. (Or allow the pasta to thaw in the refrigerator overnight and bake, covered, for 30 minutes.) Uncover and bake for 15 to 20 minutes more or until the cheese is melted and golden and a knife inserted in the center for 5 seconds comes out hot.